Integrated circuits (ICs), such as, ultra-large scale integrated (ULSI) circuits, can include as many as one million transistors or more. The ULSI circuit can include complementary metal oxide semiconductor (CMOS) field effect transistors (FETS). The transistors can include semiconductor gates disposed between drain and source regions. The drain and source regions are typically heavily doped with a P-type dopant (boron) or an N-type dopant (phosphorous).
The drain and source regions generally include a thin extension that is disposed partially underneath the gate to enhance the transistor performance. Shallow source and drain extensions help to achieve immunity to short-channel effects which degrade transistor performance for both N-channel and P-channel transistors. Short-channel effects can cause threshold voltage roll-off and drain-inducted barrier-lowering. Shallow source and drain extensions and, hence, controlling short-channel effects, are particularly important as transistors become smaller.
As transistors disposed on integrated circuits (ICs) become smaller (e.g., transistors with gate lengths approaching 50 nm), CMOS fabrication processes have utilized a two-dimensional channel-doping technique. With reference to FIG. 1, a conventional MOSFET 110 is provided on a portion 112 of an integrated circuit. MOSFET 110 is provided between insulation regions 114 and includes a source 116, a drain 118, and a gate structure 120. Gate structure 120 includes spacers 122, a dielectric layer 124, and a gate conductor 127.
Dielectric layer 124 is provided between and partially over a source extension 126 and a drain extension 128 (e.g., above a channel region 130). A silicide layer 132 is formed over gate conductor 127, source 116, and drain 118. Channel region 130 does not include a two-dimensional doping implant, wherein the channel-doping profile in the lateral direction is non-uniform and the channel-doping profile in the vertical direction is a super-steep retrograded channel-doping profile. The two-dimensional channel-doping profile is critical to scaling (i.e., proportional operation and structural elements in the ultra-small dimensions of MOSFET 110).
MOSFET 110 includes shallow pocket regions 134 and 136 which effectively suppress the short-channel effect (which degrades the robustness of the transistor to random process variations). Shallow pocket regions 134 and 136 are provided in a conventional CMOS pocket implant process. The implant process is performed after gate structure 120 is fabricated and before layer 132 is formed. Regions 134 and 136 are not deeper than source 116 and drain 118. Regions 134 and 136 are formed before extensions 126 and 128, regions 116 and 118, and spacers 122.
Pocket regions 134 and 136 should be deep enough to suppress punch through effect. However, with conventional processes, regions 134 and 136 cannot be made deep enough without forming a "halo-like structure". The disadvantages "halo-like structure" are discussed below with reference to FIG. 2.
With reference to FIG. 2, a MOSFET 134 is substantially similar to MOSFET 110, as discussed with reference to FIG. 1. However, MOSFET 134 includes deep pocket implant regions 135 and 137. Channel 130 includes a two dimensional doping implant, wherein the channel-doping profile in the lateral direction is not uniform, and the channel-doping profile in the vertical direction is a super-steep retrograded channel-doping profile. Implants 135 and 137 are formed after extensions 126 and 128, drain 116, source 118, and spacers 122 in a conventional process. The pocket implant associated with regions 135 and 137 results in a "halo-like" structure around the border of regions 116 and 118 located proximate channel region 130.
The halo-like structure of pocket regions 135 and 137 (FIG. 2) increases the doping concentration near the junction of source 116 and drain 118. Increased doping concentration near the junction of source 116 and drain 118 degrades (i.e., increases) the source/drain junction capacitance (e.g., parasitic capacitance) and, hence, reduces the speed of MOSFET 134.
Thus, there is a need for a method of forming deeper pocket regions which do not have a halo-like structure. Further still, there is a need for transistors that have locally confined deep pocket regions. Even further still, there is a need for an efficient method of manufacturing deep pocket regions for a transistor having a two-dimensional channel profile.